From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
cc: Etsuro Fujita <fujita.etsuro@lab.ntt.co.jp>,
        Andres Freund <andres@anarazel.de>,
        Ashutosh Bapat <ashutosh.bapat@enterprisedb.com>,
        Rajkumar Raghuwanshi <rajkumar.raghuwanshi@enterprisedb.com>,
        pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: Expression errors with "FOR UPDATE" and postgres_fdw with
 partition wise join enabled.
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Comments: In-reply-to Robert Haas <robertmhaas@gmail.com>
	message dated "Fri, 03 Aug 2018 09:44:52 -0400"
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Date: Fri, 03 Aug 2018 10:07:01 -0400
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Robert Haas <robertmhaas@gmail.com> writes:
> On Thu, Aug 2, 2018 at 4:25 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Now, that's a bit of a problem for postgres_fdw, because it seems to
>> insist on injecting WRVs even when the query text does not require any.
>> Why is that, and can't we get rid of it?

> I don't quite know what you mean here -- postgres_fdw does use
> whole-row vars for EPQ handling, which may be what you're thinking
> about.

As far as I can see from the example that started this thread,
postgres_fdw injects WRVs into a PWJ whether or not the query involves
FOR UPDATE; that's why this bug is reproducible in a query without FOR
UPDATE.  But we shouldn't need any EPQ support in that case.

> Honestly, I'm pretty impressed that we have added not one but two
> members to the RelOptKind enum without as little collateral damage as
> there has been.

Color me a bit more skeptical about the bug density in that, given
that enable_partitionwise_join is off by default; that means you're
not getting a lot of testing.

			regards, tom lane